DC contactor
Also known as: Main contactor
An electrically operated, remotely controlled switch in the DC path between a battery string and the PCS, used to connect or isolate the string during normal operation and faults. Unlike a manual disconnector, it is commanded by the BMS and opens automatically on protection trips such as over-current, over-voltage, or insulation fault.
In energy storage
Main contactors sit at string or rack level inside the DC block and are closed by the BMS at start-up, then opened on any fault or emergency stop. Breaking large DC currents is harder than AC because there is no natural current zero to quench the arc, so DC contactors use magnetic arc blow-out and are polarity-sensitive.